Verse 10. He that believeth on the Son of God hath the witness in himself. The evidence that Jesus is the Son of God. See Barnes "Ro 8:16".

This cannot refer to any distinct and immediate revelation of that fact, that Jesus is the Christ, to the soul of the individual, and is not to be understood as independent of the external evidence of that truth, or as superseding the necessity of that evidence; but the "witness" here referred to is the fruit of all the evidence, external and internal, on the heart, producing this result; that is, there is the deepest conviction of the truth that Jesus is the Son of God. There is the evidence derived from the fact that the soul has found peace by believing on him; from the fact that the troubles and anxieties of the mind on account of sin have been removed by faith in Christ; from the new views of God and heaven which have resulted from faith in the Lord Jesus; from the effect of this in disarming death of its terrors; and from the whole influence of the gospel on the intellect and the affections -- on the heart and the life, These things constitute a mass of evidence for the truth of the Christian religion, whose force the believer cannot resist, and make the sincere Christian ready to sacrifice anything rather than his religion; ready to go to the stake rather than to renounce his Saviour. See Barnes "1 Pe 3:15".

He that believeth not God hath made him a liar. See Barnes "1 Jo 1:10".

Because he believeth not the record, etc. The idea is, that in various ways -- at his baptism, at his death, by the influences of the Holy Spirit, by the miracles of Jesus, etc. -- God had become a witness that the Lord Jesus was sent by him as a Saviour, and that to doubt or deny this partook of the same character as doubting or denying any other testimony; that is, it was practically charging him who bore the testimony with falsehood.

{a} "witness in himself" Ro 8:16